Dear Ms Smith ------ to a married or unmarried woman
Dear John ------- to a friend or someone you know well
As the use of the first name in salutation is an informal practice, it is not recommended for more formal commercial correspondence. We do not, however, use both the first and the last name in the salutation. It is wrong to open a letter with "Dear Mr John" or "Dear Mr John Smith".
Note that Gentlemen, is the American and Dear Sirs, is the British way of opening a letter to a company when you write to a firm, not to a particular person.
1.5. The Body
The body of the letter is the message that the writer has to convey to the recipient. It begins two spaces below the salutation. The body of the letter may consist of one paragraph only, or of as many paragraphs as needed.
There should be margin at least one inch on both sides of the paper, at the top, and at the bottom. If your letter is very short, you should make your margins larger.
There is single space between lines unless the letter is very short. Double spaces are between paragraphs.
When the indented style, or modified block style with indented paragraphs is used, indent the first line of each paragraph five to ten spaces.
1.6. The Closing
The closing ends the letter. The complimentary close is two spaces below the last line of the body. Capitalize only the first word. Begin it slightly to the right of the center of the page, except in full block (完全平头式) and block style (平头式).
There are many ways to write the complimentary close. "Yours sincerely” is most commonly used. "Sincerely" is the most popular complimentary close in America. "Yours faithfully" is British usage in a letter with "Dear Sir" or "Dear Sirs" as salutation.
The way you close a letter depends on how you open it. Notice the following chart, which gives the appropriate complimentary close to use with various salutation

1.7. Signature
The signature is the signed name or mark of the person who writes the letter or the firm which he or she represents. It is written in ink immediately below the complimentary close. To sign with a rubber stamp is a form of discourtesy.
1.8. Notations (记号, 注释)
A number of notations may be included in commercial correspondence. They are special parts of a letter that supply data for the benefit of the writer or for the information of the addressee, or for the use of them both. Some notations are placed near the top of the letter and some near its bottom.
1.8.1. Reference Numbers (文号)
Reference numbers enable replies to be linked with earlier correspondence and ensure that they reach the right person or department without delay. In British style many letterheads provide spaces for references.

INTERCITY BANK Plc
----------------------------------------------------------------------------------------------------------------------
58 Jalan Thamrin, Jakarta, Indonesia
Telephone 375018 Telex 6756

Mr. S Basuki Your ref:
Jakarta Furnishings Our ref: PL/fh/246
7 Jalan Arjuna
Jakarta
12 January 1987

Dear Mr Basuki
Office furniture
We are expanding our offices in Jakarta and we will need extra desks, lights, chairs and filing cabinets.
Please send us your catalogue with your prices, sizes and colors for these items.

Yours sincerely
(Signature)
PP. Mr Peter Long
Manager
1.8.2. The Attention Line
The attention line is used when the writer of the letter addressed to a company wishes to get it delivered to the proper department or a particular person.
The attention line always follows the inside address and precedes the salutation, which for such a letter is: Gentlemen or Dear Sirs. It may be typed flush with the left margin, indented five spaces, or centered on the page. It is written either in all capital letters or underlined.
1.8.3. The Subject Line
This special part of a letter is used when the writer wants to magnify the importance of the subject. The subject line always follows the salutation and precedes the body of a letter. It may be typed flush with the left margin indented five spaces, or centered on the page. When both an attention line and a subject line are included in a letter, follow the same typing style for each. The introductory word or phrase (subject or re) is always followed by a colon.